Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B25/00—Alarm systems in which the location of the alarm condition is signalled to a central station, e.g. fire or police telegraphic systems
  • G08B25/01—Alarm systems in which the location of the alarm condition is signalled to a central station, e.g. fire or police telegraphic systems characterised by the transmission medium
  • G08B25/016—Personal emergency signalling and security systems

Definitions

• the present invention relates to an installation for transmitting alarm signals, primarily in cases of personal attack, and localizing alarm transmitters, in accordance with the preamble to the following main claim.
• radio transmitter If a radio transmitter is instead used for sending the alarm, it can be carried in the clothes and does not need to be taken out to send an alarm, since radio transmission penetrates through clothes quite easily.
• the good penetration ability of radio transmission excludes localization of the alarm sender with the help of. receivers in each room, since th,e emissions from the transmitters are not limited by the walls of a room. Attempts to localize such an emission by taking bearings is made impossible by all the reflections obtained from the building walls.
• a room code is automatically set in th alarm sender, giving its position in the building.
• the set room code i automatically changed when the alarm sender is carried from one place t another.
• the latest stored room code is sent by radio t a central alarm receiver.
• the room code received in the alarm receiver i stored in a memory and the position of the sender is shown on a digital display How coded messages are sent by radio and received and displayed in a centra receiving station is already described in the US Patent specification 3 678 391
• the room code in the alarm senders is reset as follows: A number o smalljlocally fixed transmitters, with continuous electromagnetic emission, i this case inductive emission, are placed in a building, and send a code uniqu for the position of the fixed transmitter to a receiver in each alarm sender this code therefore being called the room code.
• the received code is stored i a memory in the sender, and if the sender is triggered for sending an alarm the stored code is transmitted with the radio signal to the central alar receiver.
• Each fixed transmitter is suitably placed in one door frame so that trans mission of the room code takes place when the alarm sender is taken throug door frames between different rooms.
• the code transmitted by the fixe transmitter is thus unique for the door frame where the transmitter is placed.
• the fixed inductive transmitters for the unique code only transmit with lo power, and their transmitting antenna is a small magnetic dipole antenna Since the transmitting power is low and the field strength from a small dipol
• antenna is, in the first approximation, inversely proportional to the cube of th distance from the antenna, the clear domination of the field strength from transmitter in a door frame over the field strength from transmitters in othe door frames is thus ensured.
• a transmitter feed two dipole antennae one in each door jamb.
• Inductive transmission of the room code has been selected because it pene ⁇ trates clothes without difficulty, so that the alarm sender can be carried in a pocket, and because the propagation of the magnetic field from the dipole antenna of the fixed transmitter can be accurately calculated and limited to the areas nearest to a door opening.
• the inductive receiver for receiving the room code in a portable alarm sender will be alternately exposed to strong fields at the door openings and almost no fields at all from door to door, and sometimes to the interaction of nearly , equally as strong fields from two inductive transmitters. This results in that the inductive receiver of the alarm sender alternatingly receives strong signals having correct codes and signals with incorrect, interrupted or mixed codes. Parity bits are therefore added to the room codes, and a decoder placed in the inductive receivers of the alarm sender are adapted for reading the parity Jaits and discovering errors in the received codes. Incorrect codes will thus be rejected and not allowed to alter a room code already stored in the memory of the alarm sender.
• a dummy sender can be arranged, which is adapted to transmit a signal preventing alteration of a unique code already stored in the memory of the radio transmitter.
• Receivers for inductively transmitted, coded signals 'of ' the kind used here, their decoders and memories are known in the prior art as apparent from the US Patent specification 3 665 313.
• the portable radio transmitters in an installation are intended to send on the same radio channel with the same frequency.
• the portable alarm senders can also be provided with a memory for permanently stored code which is unique to a particular alarm sender. In emergency, this code is transmitted immediately after the code which unique to the location from which the alarm has been sent, thus indicating the alarm centre which sender and thus which person has sent the alarm.
• Figure 2 is a block diagram of an alarm sender and a central alarm receiver
• Figure 3 is a block diagram of a locally fixed transmitter
• Figure 4 is a plan of a building with examples of placing fixed transmitters.
• the installation in accordance with the invention comprises, as illustrated Figure 1, a plurality of locally fixed transmitters, of which two, 1A, IB a shown in the Figure.
• the installation further comprises one or more alar senders 2 and a central alarm receiver 3.
• the alarm sender 2 includes, as is apparent from Figure 2, an antenna 21 f receiving inductively transmitted signals; a receiver 22 with amplifier, co nected to the antenna 21; a decoder 23 for received signals; a memory 24 f storing a received code, connected to the decoder; a control logic circuit 2 operable by means of a push button 26, for controlling the transmission of t code stored in the memory 24, with the help of a radio transmitter a antenna 28, connected to the logical circuit 25.
• the central alarm receiver 3 includes a receiv antenna for radio signals, a radio receiver 32 with amplifier and a decod with indicator 33 for displaying received messages.
• t button 26 on the sender carried in the pocket of the wearer is pressed by t wearer.
• the control logic circuit 25 will thus become operable for transmit ⁇ ting, by means of the radio transmitter 27, radio signals coded with the room code stored in the memory 24 and unique to the place where the sender is at the moment.
• the alarm sender radio transmitter 27 transmits with a frequency selected in the 160 MHz-waveband " , for example.
• the radio signal from the sender is received by the central alarm receiver 3 and the unique code is shown on the display 33.
• the sender 2 is also provided with a second memory 29.
• this memory there is stored a second code unique to the individual sender, and thus also to the person carrying the sender.
• the control logic circuit 25 is adapted for sending the second code immediately after the first code when an alarm is sent.
• the display 33 in the central receiver shows the designation of the person who has sent the alarm.
• the room code stored in the memory 24 is transferred inductively to the carried alarm sender when it comes in the immediate vicinity of one of several fixed transmitters in the installation.
• each such fixed transmitter 1 there is included, as is shown in Figure 3, a modulatable oscillator 41, a code generat ⁇ or 42 with a code memory connected to the oscillator, an output amplifier 43 connected to the oscillator and a magnetic dipole antenna 44 connected to the output amplifier.
• a voltage supply unit 45 is connected to the three first- mentioned part units for supplying them with the necessary voltages.
• the fixed transmitters 1 are placed in the installation,' e g as is apparent from Figure 4.
• the figure is ⁇ plan over a building with rooms A,B,C and D. So that the fixed transmitters will act reliably on the carried alarm senders, they are placed in door frames or in other narrow passages.
• the transmitting power from the fixed transmitter, e g transmitter 51 in Figure 4 is small, and the field strength from the small dipole antenna of the transmitter is inversely proportional to the cube of the distance from the antenna, in the firs approximation,it thus being ensured that the field strength of the transmitte in a door frame clearly dominates over the field strength of transmitters i other door frames, e g transmitter 52.
• two dipole antennae 53 A, 53B may be needed, on in each door jamb and connected to the same fixed transmitter.
• a magneti loop can alternatively be arranged round the door frame instead of the dipol antennae.
• the inductive transmission enables the fixed transmitters to be manufacture in a single monolitic circuit.
• the dipole antenna, monolith and voltage suppl unit are molded together to one unit for fitting into the door jamb.
• the fixed sender 1,51 transmits a code continuously and inductively, said cod being unique to the door etc where it is placed, and when an alarm sender 2 i carried through the doorway the voltage will be sufficiently great in it receiver antenna 21 in Figure 2 for the code to be written into the sende memory 24. If the sender is subsequently carried past another fixed transmit ter, e g 52, its unique code, differing from the previous one, is transmitted and the new code is written in over the one already in the sender memory. I this way the alarm sender will always be updated with the code unique to it momentary location, and it is this code which is transmitted when an alar signal is sent.
• Parity bits are added to the typical code so that the right codes will b received in the alarm sender, in spite of strongly varying field strengths at it receiver. Reception reliability can be further increased by exchanging th latest code put into the -sender memory 24 only when two new identical an correct codes have been .received in immediate- sequence.
• the transmissio rate should be at least f Lve codes per second so that two .codes will be reliabl received during a hasty- passage through the doorway.
• the fixed transmitter transmit at a frequency selected in the range of 16-140 kHz.
• a fixed transmitter e g 54 in Figure 4
• Such unwarranted alteration of the typical code is prevented by arranging a dummy transmitter 56 between both fixed transmitters.
• the dummy 56 is substantially the same as the other fixed transmitters, but is adapted for only sending a carrier wave with the same frequency as the one from the fixed transmitters.
• the dummy transmission blocks the receiver in the alarm sender and prevents reception of such transmission which can lead to resetting the stored code.
• the dummy transmission can also be modulated to obtain greater blocking action.
• the radio transmitters of the alarm senders are normally ..adapted for transmitting at the same frequency.
• the risk of two alarm senders sending an alarm simultaneously and thus blocking each other is very small. If it is feared even so that alarms could be sent simultaneously, the risk of blocking can be reduced by making the alarm transmission short, e g 70 mS and repeating it after a comparatiavely long interval of 2 seconds. The risk of blocking is further reduced if the intervals between the alarm transmissions are made somewhat different for individual alarm senders.

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• Engineering & Computer Science (AREA)
• Computer Security & Cryptography (AREA)
• Business, Economics & Management (AREA)
• Emergency Management (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Alarm Systems (AREA)
• Burglar Alarm Systems (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20335844

Family Applications (1)

Country Status (7)

Cited By (5)

Families Citing this family (54)

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• 1978
  • 1978-09-15 SE SE7809742A patent/SE413209B/xx not_active IP Right Cessation
• 1979
  • 1979-09-13 GB GB8028642A patent/GB2051444B/en not_active Expired
  • 1979-09-13 JP JP54501549A patent/JPS6238757B2/ja not_active Expired
  • 1979-09-13 DE DE792953104T patent/DE2953104T1/de active Granted
  • 1979-09-13 WO PCT/SE1979/000188 patent/WO1980000630A1/en unknown
  • 1979-09-13 US US06/195,637 patent/US4347501A/en not_active Expired - Lifetime
  • 1979-09-13 AU AU50826/79A patent/AU527038B2/en not_active Expired

Non-Patent Citations (1)

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